Battery, method of charging and discharging the battery and charge-discharge control device for the battery

ABSTRACT

Provided is a battery capable of improving cycle characteristics through reducing a structural fracture according to charge and discharge of an anode and a reaction of the with an electrolyte. An anode active material layer includes at least one kind selected from the group consisting of a simple substance and alloys of Si capable of forming an alloy with Li. A cathode and an anode are formed so that the molar ratio Li/Si in the anode at the time of charge is 4.0 or the potential of the anode vs. Li is 0.04 V or more through adjusting, for example, a ratio between a cathode active material and an anode active material. Moreover, the cathode and the anode are formed so that the molar ratio Li/Si in the anode at the time of discharge is 0.4 or more, or the potential of the anode vs. Li is 1.4 V or less.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a battery comprising an anode whichincludes silicon (Si) as an element and is capable of inserting andextracting lithium (Li), a method of charging and discharging thebattery, and a charge-discharge control device for the battery.

2. Description of the Related Art

In recent years, as mobile devices have become more sophisticated andmultifunctional, a demand for higher capacity of secondary batteries aspower sources for the mobile devices has been made. As a secondarybattery which meets the demand, a lithium secondary battery is cited.However, in a currently typical lithium secondary battery which useslithium cobalt oxide for a cathode and graphite for an anode, itsbattery capacity has reached the saturation point, so it is extremelydifficult to significantly increase its capacity. Therefore, usinglithium metal for an anode has been considered since a long time ago;however, in order to put the anode to practical use, it is required toimprove lithium precipitation/dissolution efficiency and controldendritic deposition.

On the other hand, in recent times, a study of an anode with a highcapacity which uses silicon, germanium (Ge), tin (Sn) or the like hasbeen conducted vigorously. However, when charge and discharge arerepeated, the anode with a high capacity is broken into small pieces dueto severe expansion and shrinkage of an active material, thereby acurrent collecting property declines, and the decomposition of anelectrolyte solution is accelerated due to an increase in a surfacearea, so cycle characteristics are extremely poor. Therefore, an anodeformed through forming an active material layer on a current collectorby a vapor-phase deposition method, a liquid-phase deposition method, asintering method or the like has been studied (refer to JapaneseUnexamined Patent Application Publication No. Hei 8-50922, JapanesePatent No. 2948205, Japanese Unexamined Patent Application PublicationNos. Hei 11-135115, 2001-160392 and 2002-83594). The anode can beprevented from being broken into small pieces, compared to aconventional coating type anode formed through applying slurry includinga particulate active material, a binder and the like, and the currentcollector and the active material layer can be formed as one unit.Therefore, the electronic conductivity in the anode is extremelysuperior, and higher performance in terms of capacity and cycle lifespanis expected. Moreover, an electrical conductor, a binder and voids whichare present in a conventional anode can be reduced or eliminated, so theanode can be formed into a thin film in essence.

However, even in the anode, cycle characteristics are not sufficient,because the active material falls off due to expansion and shrinkage ofthe active material according to charge and discharge. Moreover,reactivity with an electrolyte is still high, so a reaction of the anodewith the electrolyte according to charge and discharge causes a declinein the capacity of the battery.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the invention to provide abattery capable of improving cycle characteristics through reducing astructural fracture of an anode according to charge and discharge andreactivity with an electrolyte, a method of charging and discharging thebattery, and a charge-discharge control device for the battery.

A first battery according to the invention comprises: an anode includingsilicon as an element and being capable of inserting and extractinglithium; a cathode being capable of inserting and extracting lithium;and an electrolyte, wherein a molar ratio of lithium atoms to siliconatoms (Li/Si) in the anode is 4.0 or less.

A second battery according to the invention comprises: an anodeincluding silicon as an element and being capable of inserting andextracting lithium; a cathode being capable of inserting and extractinglithium; and an electrolyte, wherein a potential of the anode vs.lithium metal as a reference potential is 0.04 V or more.

In a first method of charging and discharging a battery, the batterycomprising an anode which includes silicon as an element and is capableof inserting and extracting lithium is charged and discharged, and atthe time of charge, a molar ratio of lithium atoms to silicon atoms(Li/Si) in the anode is 4.0 or less.

In a second method of charging and discharging a battery, the batterycomprising an anode which includes silicon as an element and is capableof inserting and extracting lithium is charged and discharged, and apotential of the anode vs. lithium metal as a reference potential at thetime of charge is 0.04 V or more.

In a first charge-discharge control device for a battery, charge anddischarge of the battery comprising an anode which includes silicon asan element and is capable of inserting and extracting lithium iscontrolled, and the charge-discharge control device comprises a chargecontrol portion for controlling a molar ratio of lithium atoms tosilicon atoms (Li/Si) in the anode at the time of charge to 4.0 or less.

In a second charge-discharge control device for a battery, charge anddischarge of the battery comprising an anode which includes silicon asan element and is capable of inserting and extracting lithium iscontrolled, and the charge-discharge control device comprises a chargecontrol portion for controlling a potential of the anode vs. lithiummetal as a reference potential at the time of charge to 0.04 V or more.

In the first battery, the first method of charging and discharging abattery, and the first charge-discharge control device according to theinvention, the molar ratio of lithium atoms to silicon atoms (Li/Si) inthe anode is 4.0 or less, or in the second battery, the second method ofcharging and discharging a battery, and the second charge-dischargecontrol device according to the invention, the potential of the anodevs. lithium metal as a reference potential is 0.04 V or more, so anoverreaction between the anode and the electrolyte and a structuralfracture of the anode due to expansion and shrinkage of the anode can beprevented. Therefore, cycle characteristics can be improved.

In particular, when the molar ratio of lithium atoms to silicon atoms(Li/Si) in the anode is 0.4 or more, or when the potential of the anodevs. lithium metal as a reference potential is 1.4 V or less, the cyclecharacteristics can be further improved.

Moreover, when the electrolyte include at least one kind selected fromthe group consisting of a cyclic carbonate having an unsaturated bondand a carbonate derivative containing a halogen atom, the cyclecharacteristics can be further improved, and storage characteristics andthe like can be improved.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a secondary battery according to anembodiment of the invention;

FIG. 2 is an exploded perspective view of another secondary batteryaccording to the embodiment of the invention;

FIG. 3 is a sectional view of a spirally wound electrode body takenalong a line I-I of FIG. 2; and

FIG. 4 is a block diagram of a charge-discharge control device used inthe secondary batteries shown in FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will be described inmore detail below referring to the accompanying drawings.

FIG. 1 shows a sectional view of a secondary battery according to anembodiment of the invention. The secondary battery is a so-called cointype, and in the secondary battery, a cathode 12 contained in a packagecan 11 and an anode 14 contained in a package cup 13 are laminated witha separator 15 in between. The edge portions of the package can 11 andthe package cup 13 are caulked by an insulating gasket 16 to seal thecathode 12 and the anode 14. The package can 11 and the package cup 13are made of, for example, metal such as stainless or aluminum (Al).

The cathode 12 includes, for example, a cathode current collector 12Aand a cathode active material layer 12B disposed on the cathode currentcollector 12A. The cathode current collector 12A is made of, forexample, aluminum, nickel (Ni), stainless or the like.

The cathode active material layer 12B includes, for example, one kind ortwo or more kinds selected from cathode materials capable of insertingand extracting lithium as a cathode active material, and may include anelectrical conductor such as a carbon material and a binder such aspolyvinylidene fluoride, if necessary. As the cathode material capableof inserting and extracting lithium, for example, a lithium-containingmetal complex oxide represented by a general formula Li_(x)MIO₂ ispreferable, because as the lithium-containing metal complex oxide cangenerate a high voltage and has a high density, a higher capacity of thesecondary battery can be achieved by the lithium-containing metalcomplex oxide. In the formula, MI represents one or more kinds oftransition metals, and for example, at least one kind selected from thegroup consisting of cobalt (Co) and nickel is preferable as MI. Thevalue of x depends upon a charge-discharge state of the battery, and isgenerally within a range of 0.05≦×≦1.10. Specific examples of such alithium-containing metal complex oxide include LiCoO₂, LiNiO₂ and thelike.

The anode 14 includes, for example, an anode current collector 14A andan anode active material layer 14B disposed on the anode currentcollector 14A. The anode current collector 14A is preferably made of ametal material including at least one kind selected from metal elementswhich do not form an intermetallic compound with lithium. It is becausewhen the metal material forms an intermetallic compound with lithium,the anode current collector 14A expands and shrinks according to chargeand discharge, thereby its structural fracture occurs, so a currentcollecting property declines, and an ability of the anode currentcollector 14A to support the anode active material layer 14B is reduced,thereby the anode active material layer 14B easily falls off the anodecurrent collector 14A. In the description, the metal material includesnot only simple substances of metal elements but also an alloy includingtwo or more kinds of metal elements and an alloy including one or morekinds of metal elements and one or more kinds of metalloid elements.Examples of the metal element which does not form an intermetalliccompound with lithium include copper (Cu), nickel, titanium (Ti), iron(Fe) and chromium (Cr).

Moreover, the anode current collector 14A preferably includes a metalelement which is alloyed with the anode active material layer 14B. Aswill be described later, in the case where the anode active materiallayer 14B includes silicon as an element, the anode active materiallayer 14B largely expands and shrinks according to charge and discharge,thereby the anode active material layer 14B easily falls off the anodecurrent collector 14A; however, when the anode active material layer 14Bis alloyed with the anode current collector 14A to firmly bond themtogether, the anode active material layer 14B can be prevented fromfalling off the anode current collector 14A. As a metal element whichdoes not form an intermetallic compound with lithium and is alloyed withthe anode active material layer 14B, for example, as a metal elementalloyed with silicon, copper, nickel and iron are cited. In terms ofstrength and conductivity, they are preferable.

The anode current collector 14A may have a single layer or a pluralityof layers. In the case where the anode current collector 14A has aplurality of layers, a layer making contact with the anode activematerial layer 14B may be made of a metal material being alloyed withthe anode active material layer 14B, and other layers may be made of anyother metal material. Moreover, the anode current collector 14A ispreferably made of a metal material including at least one kind selectedfrom metal elements which do not form an intermetallic compound withlithium, except for an interface with anode active material layer 14B.

As an anode active material, the anode active material layer 14Bincludes, for example, one kind or two or more kinds selected from anodematerials which are capable of inserting and extracting lithium andinclude silicon as an element, because silicon has a large ability toinsert and extract lithium and can obtain a high energy density. Siliconmay be included in the form of a simple substance, an alloy or acompound. The silicon content in the anode active material layer 14B ispreferably 50 mol% or more, more preferably 75 mol% or more, and morepreferably 90 mol% or more, because the capacity can be increased.

Examples of the alloy or the compound of silicon include an alloy or acompound including boron (B), magnesium (Mg), aluminum, phosphorus (P),calcium (Ca), titanium, vanadium (V), chromium, manganese (Mn), iron,cobalt, nickel, copper, zinc (Zn), germanium (Ge), zirconium (Zr),niobium (Nb), molybdenum (Mo), palladium (Pd), silver (Ag), tin (Sn),antimony (Sb), tantalum (Ta), tungsten (W), barium (Ba) or the like inaddition to silicon.

More specifically, SiB₄, SiB₆, Mg₂Si, Ni₂Si, NiSi₂, TiSi₂, MoSi₂, CoSi₂,CaSi₂, CrSi₂, Cu₅Si, FeSi₂, MnSi₂, NbSi₂, TaSi₂, VSi₂, WSi₂, ZnSi₂, SiC,Si₃N₄, SiW, Si₄W, Si_(0.95)W_(0.05), Si₄Cu, Si_(0.95)Mo_(0.05),Si_(0.99)B_(0.01), Si_(0.995)P_(0.005), Si_(0.9)Zn_(0.1) and the likeare cited. They are indicated by a molar ratio.

The anode active material layer 14B is preferably formed by at least onekind selected from the group consisting of a vapor-phase depositionmethod, a liquid-phase deposition method and a sintering method, becausea fracture of the anode active material layer 14B due to expansion andshrinkage thereof according to charge and discharge can be prevented,and the anode current collector 14A and the anode active material layer14B can be formed as one unit, and the electronic conductivity in theanode active material layer 14B can be improved. Moreover, it is becausea binder and voids can be reduced or eliminated, and the anode 14 can beformed into a thin film. In the description, “an active material layeris formed by a sintering method” means that a layer formed throughmixing powder including an active material and a binder is heated in anonoxidizing atmosphere or the like to form a denser layer with a highervolume density, compared to the layer before the heat treatment.

The anode active material layer 14B may be formed through coating, andmore specifically, the anode active material layer 14B may include ananode active material and, if necessary, a binder such as polyvinylidenefluoride. However, the anode active material layer 14B formed by atleast one kind selected from the group consisting of a vapor-phasedeposition method, a liquid-phase deposition method and a sinteringmethod is more preferable.

The anode active material layer 14B is preferably alloyed with the anodecurrent collector 14A at at least a part of an interface with the anodecurrent collector 14A so that the anode active material layer 14B can beprevented from falling off the anode current collector 14A due toexpansion and shrinkage. More specifically, it is preferable that anelement of the anode current collector 14A is diffused into the anodeactive material layer 14B, or an element of the anode active materiallayer 14B is diffused into the anode current collector 14A, or they arediffused into each other at an interface therebetween. When the anodeactive material layer 14B is formed by a vapor-phase deposition method,a liquid-phase deposition method or a sintering method, alloying oftenoccurs at the same time; however, alloying may occur by further heattreatment. In the description, the above-described diffusion of theelements is considered as a mode of alloying.

Moreover, in the secondary battery, for example, the ratio between theamount of the cathode active material and the amount of the anode activematerial is adjusted so as to control the amount of lithium to beinserted into the anode 14 during charge. More specifically, the ratiobetween the amount of the cathode active material and the amount of theanode active material is adjusted so that a molar ratio of lithium atomsto silicon atoms (hereinafter referred to as Li/Si ratio) in the anode14 becomes 4.0 or less at the end of charge, or the potential of theanode 14 vs. lithium metal as a reference potential (hereinafterreferred to as potential vs. Li) becomes 0.04 V or more at the end ofcharge. It is because when the amount of lithium to be inserted into theanode 14 is limited, an overreaction between the anode 14 and anelectrolyte solution and the structural fracture of the anode 14 due toexpansion and shrinkage can be prevented. The potential of the anode 14vs. Li means a potential measured through taking the anode 14 out of thesecondary battery, and then using the anode 14 as a working electrodeand a lithium metal plate as a counter electrode.

The Li/Si ratio in the anode 14 at the end of charge is preferablyadjusted to be 3.7 or less, and more preferably 3.5 or less. Moreover,the potential of the anode 14 vs. Li at the end of charge is morepreferably adjusted to be 0.08 V or more, and more preferably 0.1 V ormore. It is because cycle characteristics can be further improved.However, the smaller the Li/Si ratio is, or the larger the potential vs.Li is, the more the battery capacity will decline, so the Li/Si ratio atthe end of charge is preferably adjusted to be at least 3.5 or more, orthe potential vs. Li at the end of charge is preferably adjusted to beat least 0.1 V or less.

The Li/Si ratio in the anode 14 or the potential of the anode 14 vs. Lican be measured through taking the anode 14 out of the secondarybattery, and then analyzing the anode active material layer 14B by anICP (Inductively Coupled Plasma) method or measuring the capacity or thepotential of the anode 14 by using the anode 14 as a working electrodeand a lithium metal plate as a counter electrode.

The amount of lithium to be inserted into the anode 14 at the time ofcharge can be reduced, when the molar ratio of the cathode activematerial to the anode active material (the cathode active material/theanode active material) is reduced. A preferable molar ratio of thecathode active material to the anode active material depends upon kindsof the anode active material and cathode active material, or the like.

Moreover, in the secondary battery, for example, it is preferable thatlithium is inserted into the anode 14 in advance to control the amountof lithium remaining in the anode 14 at the time of discharge. Morespecifically, the Li/Si ratio in the anode 14 at the end of discharge ispreferably adjusted to be 0.4 or more, or the potential of the anode 14vs. Li at the end of discharge is preferably adjusted to be 1.4 V orless. It is because when lithium remains in the anode 14, the expansionand shrinkage of the anode 14 can be reduced and the structural fracturecan be prevented.

The Li/Si ratio in the anode 14 at the end of discharge is morepreferably adjusted to be 0.43 or more, and more preferably 0.46 ormore. Moreover, the potential of the anode 14 vs. Li at the end ofdischarge is preferably adjusted to be 1.2 V or less, and morepreferably 1.1 V or less. It is because the cycle characteristics can befurther improved. However, the more the Li/Si ratio increases, or themore the potential vs. Li is reduced, the more the battery capacity willdecline, so it is preferable that at the end of discharge, the Li/Siratio is adjusted to be at least 0.46 or less, and the potential vs. Liis adjusted to be at least 1.1 or more.

The separator 15 isolates the cathode 12 from the anode 14 to passlithium ions therethrough while preventing a short circuit of currentdue to contact between the cathode 12 and the anode 14. The separator 15is made of, for example, polyethylene or polypropylene.

The separator 15 is impregnated with an electrolyte solution which is aliquid electrolyte. The electrolyte solution includes, for example, asolvent and a lithium salt as an electrolyte salt dissolved in thesolvent, and may include various additives if necessary. As the solvent,a nonaqueous solvent is preferable, and, for example, an organic solventtypified by a carbonate such as ethylene carbonate, propylene carbonate,dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate iscited. One kind or a mixture of two or more kinds selected from them maybe used. For example, a mixture including a high-boiling point solventsuch as ethylene carbonate or propylene carbonate and a low-boilingpoint solvent such as dimethyl carbonate, diethyl carbonate or ethylmethyl carbonate is preferably used, because high ionic conductivity canbe obtained.

As the solvent, a carbonate derivative containing a halogen atom is alsocited, and the carbonate derivative containing a halogen atom ispreferably used, because higher cycle characteristics can be obtained,and storage characteristics can be improved. In this case, the carbonatederivative containing a halogen atom may be used singly or incombination with any other solvent such as the above-described solvent.As the carbonate derivative containing a halogen atom,4-fluoro-1,3-dioxolane-2-one, 4-chloro-1,3-dioxolane-2-one,4-bromo-1,3-dioxolane-2-one, 4,5-difluoro-1, 3-dioxolane-2-one and thelike are cited, and among them, 4-fluoro-1,3-dioxolane-2-one ispreferable, because a higher effect can be obtained.

As the solvent, a cyclic carbonate having an unsaturated bond is alsocited, and the cyclic carbonate is preferably used in combination withany other solvent, because higher cycle characteristics can be obtained.As the cyclic carbonate having an unsaturated bond, 1,3-dioxol-2-one or4-vinyl-1,3-dioxolane-2-one or the like is cited.

As the lithium salt, for example, LiPF₆, LiClO₄, LiCF₃SO₃, Li(CF₃SO₂)₂N,Li(C₂F₅SO₂)₂N, lithium bis(oxalato) borate shown in Chemical Formula 1or lithium difluoro[oxalato-O,O′] borate shown in Chemical Formula 2 iscited, and one kind or a mixture of two or more kinds selected from themmay be used.

The battery can be manufactured through the following steps, forexample.

At first, for example, a cathode active material, an electricalconductor and a binder are mixed to prepare a mixture, and then themixture is dispersed in a dispersion medium such asN-methyl-2-pyrrolidone to form mixture slurry. Then, after the mixtureslurry is applied to the cathode current collector 12A, the mixtureslurry is compression molded to form the cathode active material layer12B, thereby the cathode 12 is formed.

Next, for example, the anode active material is deposited on the anodecurrent collector 14A by a vapor-phase deposition method or aliquid-phase deposition method to form the anode active material layer14B, thereby the anode 14 is formed. Alternatively, the anode activematerial layer 14B may be formed by a sintering method in which after aprecursor layer including a particulate anode active material is formedon the anode current collector 14A, the precursor layer is sintered, orthe anode active material layer 14B may be formed by a combination oftwo or three methods selected from the group consisting of a vapordeposition method, a liquid-phase deposition method and a sinteringmethod. Further, the anode active material layer 14B may be formedthrough mixing a particulate anode active material, an electricalconductor and a binder to form a mixture, dispersing the mixture in adispersion medium such as N-methyl-2-pyrrolidone to form mixture slurry,applying the mixture slurry to the anode current collector 14A, andcompression molding the mixture slurry. Through the use of at least onemethod selected from the group consisting of a vapor-phase depositionmethod, a liquid-phase deposition method and a sintering method, in somecases, the anode active material layer 14B alloyed with the anodecurrent collector 14A at at least a part of an interface with the anodecurrent collector 14A is formed. In order to further alloy between theanode current collector 14A and the anode active material layer 14B atthe interface, a heat treatment in a vacuum atmosphere or a nonoxidizingatmosphere may be further performed.

As the vapor-deposition method, for example, a physical depositionmethod or a chemical deposition method are used, and more specifically,a vacuum deposition method, a sputtering method, an ion plating method,a laser ablation method, a CVD (Chemical Vapor Deposition) method, aspraying method or the like can be used. As the liquid-phase depositionmethod, a known method such as an electrolytic plating method or anelectroless plating method can be used. As the sintering method, a knowntechnique such as, for example, an atmosphere sintering method, areaction sintering method or a hot press sintering method can be used.

When the cathode 12 and the anode 14 are formed, the amount of thecathode active material and the amount of the anode active material areadjusted so that, as described above, the Li/Si ratio in the anode 14 atthe time of charge becomes 4.0 or less or the potential of the anode 14vs. Li at the time of charge becomes 0.04 V or more. Moreover, it ispreferable that lithium is inserted into the anode 14, and, as describedabove, the Li/Si ratio in the anode 14 at the time of discharge becomes0.4 or more, or the potential of the anode 14 vs. Li at the time ofdischarge becomes 1.4 V or less.

Next, for example, the cathode 12, the separator 15 impregnated with theelectrolyte solution, and the anode 14 are laminated and put into thepackage can 11 and the package cup 13, and they are caulked. Thereby,the secondary battery shown in FIG. 1 can be obtained.

FIG. 2 shows another secondary battery according to the embodiment ofthe invention. The secondary battery is a so-called winding type, and inthe secondary battery, a spirally wound electrode body 30 to which leads21 and 22 are attached is contained in film-shaped package members 41and 42, thereby the secondary battery can be formed with a smaller size,a lighter weight and a lower profile.

The leads 21 and 22 are drawn from the interiors of the package members41 and 42 to outside, for example, in the same direction. The leads 21and 22 are made of, for example, a metal material such as aluminum,copper, nickel or stainless in a sheet shape or a mesh shape.

The package members 41 and 42 are made of, for example, a rectangularaluminum laminate film including a nylon film, aluminum foil and apolyethylene film which are bonded in this order. The package members 41and 42 are disposed so that the polyethylene film of each of the packagemembers 41 and 42 faces the spirally wound electrode body 30, and edgeportions of the package members 41 and 42 are adhered to each other byfusion bonding or an adhesive. An adhesive film 43 is inserted eachbetween the package member 41 and the lead 21, between the packagemember 41 and the lead 22, between the package member 42 and the lead 21and between the package member 42 and the lead 22 for preventing theentry of outside air. The adhesive film 43 is made of, for example, amaterial having adhesion to the leads 21 and 22, that is, a polyolefinresin such as polyethylene, polypropylene, modified polyethylene ormodified polypropylene.

In addition, the package members 41 and 42 may be made of a laminatefilm with any other structure, a polymeric film such as polypropylene ora metal film instead of the aluminum laminate film.

FIG. 3 shows a sectional view of the spirally wound electrode body 30taken along a line I-I of FIG. 2. The spirally wound electrode body 30is a spirally wound laminate including a cathode 31 and an anode 32 witha separator 33 and an electrolyte layer 34 in between, and an outermostportion of the spirally wound electrode body 30 is protected with aprotective tape 35.

The cathode 31 has a structure in which a cathode active material layer31B is disposed on one side or both sides of a cathode current collector31A. The anode 32 has a structure in which an anode active materiallayer 32B is disposed on one side or both sides of an anode currentcollector 32A, and the anode active material layer 32B and the cathodeactive material layer 31B are disposed so as to face each other. Thestructures of the cathode current collector 31A, the cathode activematerial layer 31B, the anode current collector 32A, the anode activematerial layer 32B and the separator 33 are the same as those of thecathode current collector 12A, the cathode active material layer 12B,the anode current collector 14A, the anode active material layer 14B andthe separator 15, respectively.

The electrolyte layer 34 is made of a so-called gel electrolyte in whicha holding body holds an electrolyte solution. The gel electrolyte ispreferable, because the gel electrolyte can obtain high ionicconductivity, and can prevent leakage of the battery or expansion due tohigh temperature. The structure of the electrolyte solution is the sameas that in the coin type secondary battery shown in FIG. 1. The holdingbody is made of, for example, a polymeric material. As the polymericmaterial, for example, polyvinylidene fluoride is cited.

The secondary battery can be manufactured through the following steps,for example.

At first, the cathode 31 and the anode 32 are formed in the same manneras those in the above-described coin-type secondary battery, and theelectrolyte layer 34 in which a holding body holds an electrolytesolution is formed on the cathode active material layer 31B and theanode active material layer 32B. Next, the lead 21 is attached to an endportion of the cathode current collector 31A through welding, and thelead 22 is attached to an end portion of the anode current collector 32Athrough welding. Then, after the cathode 31 on which the electrolytelayer 34 is formed and the anode 32 on which the electrolyte layer 34 isformed are laminated with the separator 33 in between to form a laminatebody, the laminate body is spirally wound in a longitudinal direction,and the protective tape 35 is bonded to an outermost portion of thelaminate body so as to form the spirally wound electrode body 30. Afterthat, the spirally wound electrode body 30 is sandwiched between thepackage members 41 and 42, and edge portions of the package members 41and 42 are adhered to each other through thermal fusion bonding or thelike to seal the spirally wound electrode body 30 in the package members41 and 42. At this time, the adhesive film 34 is inserted each betweenthe lead 21 and the package member 41, between the lead 21 and thepackage member 42, between the lead 22 and the package member 41 andbetween the lead 22 and the package member 42. Thereby, the secondarybattery shown in FIGS. 2 and 3 is completed.

Moreover, the secondary battery may be manufactured through thefollowing steps. At first, after the cathode 31 and the anode 32 areformed, the leads 21 and 22 are attached. Next, the cathode 31 and theanode 32 are laminated with the separator 33 in between to form alaminate, and the laminate is spirally wound. Then, the protective tape35 is bonded to an outermost portion of the laminate so as to form aspirally wound body as a precursor body of the spirally wound electrodebody 30. Next, the spirally wound body is sandwiched between the packagemembers 41 and 42, and the edge portions of the package members 41 and42 except for one side are adhered through thermal fusion bonding toform a pouched package. Then, components for an electrolyte whichinclude the electrolyte solution, a monomer as a material of a polymericcompound and a polymerization initiator and, if necessary, any othermaterial such as a polymerization inhibitor are injected in the packagemembers 41 and 42. After that, an opened portion of the package members41 and 42 are sealed through thermal fusion bonding under a vacuumatmosphere, and the monomer is polymerized through applying heat to formthe polymeric compound, thereby the gel electrolyte layer 34 is formed.Thereby, the secondary battery shown in FIGS. 2 and 3 is completed.

These secondary batteries are used in, for example, mobile electronicdevices such as cellular phones and portable personal computers.

At this time, a charge-discharge control device for controlling chargeand discharge may be mounted in a mobile electronic device together withthe secondary battery. When the charge-discharge control device is used,even if the structures of the cathodes 12 and 31 and the anodes 14 and32 are not adjusted as described above, in some cases, the Li/Si ratiosin the anodes 14 and 32 or the potentials of the anodes 14 and 32 vs. Liat the time of charge and discharge can be controlled as describedabove. However, charge and discharge may not be able to be controlled asdescribed above only by the charge-discharge control device, and whencharge and discharge is controlled only by the charge-discharge controldevice, the battery voltage will decline, so it is preferable that thecathodes 12 and 31 and the anodes 14 and 32 are adjusted as describedabove.

FIG. 4 shows the structure of the charge-discharge control device usedin the above-described secondary batteries. A charge-discharge controldevice 50 comprises a connecting terminal 51 for connecting to a powersupply such as a home AC power supply (not shown), a connecting terminal52 for connecting to a secondary battery 60, and a connecting terminal53 for connecting to an electronic device or the like. Moreover, thecharge-discharge control device 50 comprises a power supply circuitportion 54 connected to the connecting terminal 51, a charge controlportion 55 connected to the power supply circuit portion 54 and theconnecting terminal 52 and a discharge control portion 56 connected tothe connecting terminals 52 and 53.

The power supply circuit portion 54 converts a power supply voltagesupplied from the power supply into a predetermined DC voltage, andstably supplies the voltage to the charge control portion 55, andincludes a so-called AC-DC converter.

The charge control portion 55 controls charge on the secondary battery60, and includes, for example, a constant current charge means forcarrying out constant-current charge, a constant-voltage chargeconversion control means for converting from constant-current charge toconstant-voltage charge when the battery voltage reaches a predeterminedconstant-voltage conversion value during constant-current charge, aconstant-voltage charge means for carrying out constant-voltage charge,and a charge termination control means for terminating charge when acurrent value reaches a predetermined charge termination value duringconstant-voltage charge.

The constant-voltage charge conversion value in the constant-voltagecharge conversion control means is set to a battery voltage value atwhich the Li/Si ratios in the anodes 14 and 32 become 4.0 or less, orthe potentials of the anodes 14 and 42 vs. Li become 0.04 V or more onthe basis of, for example, a relationship between a battery voltagedetermined by charge-discharge curves of the cathodes 12 and 31 andcharge-discharge curves of the anodes 14 and 32, and the Li/Si ratios inthe anodes 14 and 32 or the potentials of the anodes 14 and 32 vs. Li.More preferably, the constant-voltage charge conversion value is set toa battery voltage value at which the Li/Si ratios in the anodes 14 and32 become 3.7 or less, or the potentials of the anodes 14 and 32 vs. Libecome 0.08 V or more, and more preferably, a battery voltage value atwhich the Li/Si ratios in the anodes 14 and 32 become 3.5 or less, orthe potentials of the anodes 14 and 32 vs. Li become 0.1 V or more.However, as described above, in order to increase the battery capacity,the constant-voltage charge conversion value is preferably set to abattery voltage value at which the Li/Si ratio becomes 3.5 or more, orthe potential vs. Li becomes 0.1 V or less.

The discharge control portion 56 controls discharge on the secondarybattery, and includes a constant-current discharge means for carryingout constant-current discharge and a discharge termination control meansfor terminating discharge when the battery voltage reaches apredetermined discharge termination value. The discharge terminationvalue in the discharge termination control means is set to a batteryvoltage value at which the Li/Si ratios in the anodes 14 and 32 become0.4 or more, or the potentials of the anodes 14 and 32 vs. Li become 1.4V or less on the basis of a relationship between a battery voltagedetermined in the same manner as in the case of the constant-voltagecharge conversion value, and the Li/Si ratios in the anodes 14 and 32 orthe potentials of the anodes 14 and 32 vs. Li. More preferably, thedischarge termination value is set to a battery voltage value at whichthe Li/Si ratios in the anodes 14 and 32 become 0.43 or more or thepotentials of the anodes 14 and 32 vs. Li become 1.2 V or less, and morepreferably the Li/Si ratios in the anodes 14 and 32 become 0.46 or moreor the potentials of the anodes 14 and 32 become 1.1 V or less. However,as described above, the discharge termination value is preferably set toa battery voltage value at which the Li/Si ratio becomes 0.46 or less,or the potential vs. Li becomes 1.1 V or more.

The secondary battery 60 is charged and discharged through, for example,the following steps by such a charge-discharge control device 50.

At the time of charge, a power supply voltage supplied from a powersupply is converted into a predetermined DC voltage and the voltage issupplied to the charge control portion 55 by the power supply circuitportion 54, then charge is controlled by the charge control portion 55.More specifically, at first, constant-current charge is carried out bythe constant-current charge means. At this time, the battery voltage ismonitored by the constant-voltage charge conversion control means, andwhen the battery voltage reaches the constant-voltage charge conversionvalue, charge is converted into constant-voltage charge. Next,constant-voltage charge is carried out by the constant-voltage chargemeans, and the current value is monitored by the charge terminationcontrol means. When the current value reaches the charge terminationvalue, charge is terminated. The constant-voltage charge conversionvalue is set to, for example, a battery voltage at which the Li/Siratios in the anodes 14 and 32 become 4.0 or less or the potentials ofthe anodes 14 and 32 vs. Li become 0.04 V or more, so the Li/Si ratiosin the anodes 14 and 32 at the time of charge are controlled to 4.0 orless, or the potentials of the anodes 14 and 32 vs. Li at the time ofcharge are controlled to 0.04 V or more.

At the time of discharge, discharge is controlled by the dischargecontrol portion 56. More specifically, constant-current discharge iscarried out by the constant-current discharge means, and the batteryvoltage is monitored by the discharge termination control means. Whenthe battery voltage reaches the discharge termination value, dischargeis terminated. The discharge termination value is set to, for example, abattery voltage at which the Li/Si ratios in the anodes 14 and 32 become0.4 or more or the potentials of the anodes 14 and 32 vs. Li become 1.4V or less, thereby the Li/Si ratios in the anodes 14 and 32 at the timeof discharge are controlled to 0.4 or more, or the potentials of theanodes 14 and 32 vs. Li are controlled to 1.4 V or less.

Thus, in the embodiment, the Li/Si ratios in the anodes 14 and 32 are4.0 or less, or the potentials of the anodes 14 and 32 vs. Li are 0.04 Vor more, so an overreaction between the anodes 14 and 32 and theelectrolyte and the structural fracture of the anodes 14 and 32 due toexpansion and shrinkage can be prevented. Therefore, cyclecharacteristics can be improved.

In particular, when the Li/Si ratios in the anodes 14 and 32 are 3.7 orless, or the potentials of the anodes 14 and 32 vs. Li are 0.08 V ormore, and more specifically, when the Li/Si ratios in the anodes 14 and32 at the end of charge are 3.5 or less, or the potential of the anodes14 and 32 vs. Li at the end of charge is 0.1 V or more, a higher effectcan be obtained.

Moreover, when the Li/Si ratios in the anodes 14 and 32 are 0.4 or more,or the potentials of the anodes 14 and 32 vs. Li are 1.4 V or less,expansion and shrinkage of the anodes 14 and 32 can be reduced, therebythe structural fracture of the anodes 14 and 32 can be more effectivelyprevented.

Further, when the Li/Si ratios in the anodes 14 and 32 are 0.43 or more,or the potentials of the anodes 14 and 32 vs. Li are 1.2 V or less, andmore specifically when the Li/Si ratios in the anodes 14 and 32 are 0.46or more, or the potentials of the anodes 14 and 32 vs. Li are 1.1 V orless, a higher effect can be obtained.

In addition, when the electrolyte includes at least one kind selectedfrom the group consisting of a cyclic carbonate having an unsaturatedbond and a carbonate derivative containing a halogen atom, the cyclecharacteristics can be further improved, and storage characteristics andthe like can be improved.

Examples

Examples of the invention will be described in detail below referring tothe drawings. In the following examples, like components are donated bylike numerals as of the above embodiment.

Examples 1-1 through 1-6

Coin-type secondary batteries with a diameter of 20 mm and a thicknessof 16 mm shown in FIG. 1 were formed. The cathode 12 was formed throughthe following steps. At first, lithium carbonate (LiCO₃) and cobaltcarbonate (CoCO₃) were mixed at a molar ratio of LiCO₃:CoCO₃=0.5:1 toform a mixture, and the mixture was fired for 5 hours at 900° C. in airto obtain lithium cobalt oxide (LiCoO₂) as a cathode active material.Next, the lithium cobalt oxide, graphite as an electrical conductor andpolyvinylidene fluoride as a binder were mixed at a mass ratio oflithium cobalt oxide:graphite:polyvinylidene fluoride=91:6:3 to form amixture. Next, the mixture was dispersed in N-methyl-2-pyrrolidone as adispersion medium to form mixture slurry, and the mixture slurry wasapplied to the cathode current collector 12A made of aluminum foil witha thickness of 20 μm, and dried, the mixture slurry was pressurized toform the cathode active material layer 12B, and then the cathode currentcollector 12A and the cathode active material layer 12B were stampedinto a circular shape with a diameter of 15 mm.

Moreover, the anode 14 was formed as follows. At first, silicon isdeposited on the anode current collector 14A made of electrolytic copperfoil having an arithmetic mean roughness (Ra) of 0.5 μm and a thicknessof 35 μm by a vapor deposition method to form the anode active materiallayer 14B. After the anode active material layer 14B was heated in avacuum, and dried, the anode current collector 14A and the anode activematerial layer 14B were stamped into a circular shape with a diameter of16 mm.

At that time, a ratio between the amount of the cathode active materiallayer 12B and the amount of the anode active material layer 14B, thatis, a molar ratio of the cathode active material to the anode activematerial was changed in Examples 1-1 through 1-6, thereby the Li/Siratio in the anode 14 or the potential of the anode 14 vs. Li at the endof charge and at the end of discharge was changed.

The formed cathode 12 and the formed anode 14 with the separator 15 madeof a polyethylene film in between were mounted on the package can 11,and the electrolyte solution was injected from above, and the packagecup 13 was laid on the package can 11, and the package can 11 and thepackage cup 13 were caulked to seal the cathode 12 and the anode 14. Asthe electrolyte solution, an electrolyte solution including a solventwhich included ethylene carbonate (EC) and dimethyl carbonate (DMC) at amass ratio of 1:1, and LiPF₆ as a lithium salt which was dissolved inthe solvent at a concentration of 1 mol/l was used.

A charge-discharge test was carried out on the secondary batteries ofExamples 1-1 through 1-6 at 25° C. to determine their capacity retentionratios in the 100th cycle. The capacity retention ratio in the 100thcycle was determined as a ratio of a discharge capacity in the 100thcycle to the initial discharge capacity, that is, (the dischargecapacity in the 100th cycle/the initial discharge capacity) %100. Atthat time, the secondary batteries were charged at a constant currentdensity of 1 mA/cm² until a battery voltage reached 4.2 V, then chargewas continued at a constant voltage of 4.2 V until a current densityreached 0.04 mA/cm². Then, the secondary batteries were discharged at aconstant current density of 1 mA/cm² until the battery voltage reached 2V to 3 V so that the Li/Si ratio in the anode 14 at the end of dischargebecame 0.4 or more or the potential of the anode 14 vs. Li at the end ofdischarge became 1.4 V or less.

In other words, in Examples 1-1 through 1-6, while the molar ratio ofthe cathode active material to the anode active material was adjusted sothat at a battery voltage of 4.2 V, the Li/Si ratio in the anode 14 atthe end of charge became 4.0 or less or the potential of the anode 14vs. Li became 0.04 V or more, a relationship between the battery voltageat the time of discharge, the Li/Si ratio in the anode 14 and thepotential of the anode 14 vs. Li was determined by a charge-dischargecurve of the cathode 12 and a charge-discharge curve of the anode 14,and a discharge termination value at which discharge is terminated wasset so that the Li/Si ratio in the anode 14 at the end of dischargebecame 0.4 or more or the potential of the anode 14 vs. Li at the end ofdischarge became 1.4 V or less.

Moreover, the anode 14 was taken out of each of the secondary batteriesof Examples 1-1 through 1-6 after charge under the above conditions andafter discharge under the above conditions to analyze the Li/Si ratio inthe anode active material layer 14B by an ICP method. Further, the anode14 was taken out after charge under the above conditions and afterdischarge under the above conditions, and then the potential of theanode 14 was measured by using the anode 14 as a working electrode and alithium metal plate as a counter electrode. The obtained results areshown in Table 1. TABLE 1 AT THE END AT THE END OF CHARGE OF DISCHARGELi/Si Li/Si RATIO IN POTENTIAL RATIO IN POTENTIAL CAPACITY METHOD OFANODE OF ANODE ANODE OF ANODE RETENTION FORMING (MOLAR VS. Li (MOLAR VS.Li RATIO ANODE RATIO (V) RATIO (V) (%) EXAMPLE 1-1 VAPOR 4.0 0.04 0.401.4 70.1 DEPOSITION EXAMPLE 1-2 VAPOR 3.95 0.05 0.41 1.3 71.4 DEPOSITIONEXAMPLE 1-3 VAPOR 3.8 0.07 0.41 1.3 81.4 DEPOSITION EXAMPLE 1-4 VAPOR3.5 0.1 0.43 1.2 94.8 DEPOSITION EXAMPLE 1-5 VAPOR 3.5 0.1 0.46 1.1 95.8DEPOSITION EXAMPLE 1-6 VAPOR 3.7 0.08 0.46 1.1 90.4 DEPOSITIONCOMPARATIVE VAPOR 4.3 0.01 0.38 1.5 47.5 EXAMPLE 1-1 DEPOSITIONElectrolyte solution: EC + DMC + LiPF₆

As Comparative Example 1-1 relative to Example 1-1 through 1-6, asecondary battery was formed as in the case of Examples 1-1 through 1-6,except that the molar ratio of the cathode active material to the anodeactive material was changed. A charge-discharge test was carried out onthe secondary battery of Comparative Example 1-1 as in the case ofExamples 1-1 through 1-6 to determine its capacity retention ratio inthe 100th cycle and measure the Li/Si ratio in the anode and thepotential of the anode vs. Li after charge under the above conditionsand after discharge under the above conditions. The results are alsoshown in Table 1.

It was obvious from Table 1 that in Examples 1-1 through 1-6 in whichthe Li/Si ratio in the anode 14 at the end of charge was 4.0 or less, orthe potential of the anode 14 vs. Li at the end of charge was 0.04 V ormore and the Li/Si ratio in the anode 14 at the end of discharge was 0.4or more or the potential of the anode 14 vs. Li at the end of dischargewas 1.4 V or less, a higher capacity retention ratio was obtained,compared to Comparative Example 1-1. Moreover, when the Li/Si ratio inthe anode 14 at the end of charge was 3.7 or less or the potential ofthe anode 14 vs. Li at the end of charge was 0.08 V or more, and theLi/Si ratio in the anode 14 at the end of discharge was 0.43 or more orthe potential of the anode 14 vs. Li at the end of discharge was 1.2 Vor less, a higher capacity retention ratio of 90% or more was obtained,and when the Li/Si ratio in the anode 14 was 3.5 or the potential of theanode 14 vs. Li was 0.1 V, and the Li/Si ratio in the anode 14 at theend of discharge was 0.46 or the potential of the anode 14 vs. Li at theend of discharge was 1.1 V, the highest capacity retention ratio wasobtained.

In other words, it was found out that when the Li/Si ratio in the anode14 at the end of charge was 4.0 or less, or the potential of the anode14 vs. Li at the end of charge was 0.04 V or more, and the Li/Si ratioin the anode 14 at the end of discharge was 0.4 or more, or thepotential of the anode 14 vs. Li at the end of discharge was 1.4 V orless, cycle characteristics could be improved. Moreover, it was foundout that when the Li/Si ratio in the anode 14 at the end of charge was3.7 or less or the potential of the anode 14 vs. Li at the end of chargewas 0.08 V or more, and more specifically when the Li/Si ratio in theanode 14 at the end of charge was 3.5, or the potential of the anode 14vs. Li at the end of charge was 0.1 V, or when the Li/Si ratio in theanode 14 at the end of discharge was 0.43 or more, or the potential ofthe anode 14 vs. Li at the end of discharge was 1.2 V or less, and morespecifically when the Li/Si ratio in the anode 14 at the end ofdischarge was 0.46, or the potential of the anode 14 vs. Li at the endof discharge was 1.1 V, higher cycle characteristics could be obtained.

Examples 2-1 through 2-3

Secondary batteries were formed as in the case of Example 1-5 or Example1-6, except that the composition of the electrolyte solution waschanged. As the electrolyte solution, an electrolyte solution formedthrough adding 1,3-dioxol-2-one (VC) or 4-vinyl-1,3-dioxolane-2-one(VEC) to the electrolyte solution used in Examples 1-1 through 1-6, thatis, the electrolyte solution including the solvent which includedethylene carbonate and dimethyl carbonate at a mass ratio of 1:1 andLiPF₆ which was dissolved in the solvent at a concentration of 1 mol/lwas used. At that time, the contents of VC and VEC in the electrolytesolution were changed as shown in Tables 2 and 3 in Examples 2-1 through2-3.

A charge-discharge test was carried out on the secondary batteries ofExamples 2-1 through 2-3 as in the case of Examples 1-5 and 1-6 todetermine their capacity retention ratios in the 100th cycle and measurethe Li/Si ratio in the anode 14 and the potential of the anode 14 vs. Liafter charge under the above conditions and after discharge under theabove conditions. The obtained results are shown in Tables 2 and 3together with the results of Examples 1-5 and 1-6. TABLE 2 AT THE END OFAT THE END OF CHARGE DISCHARGE Li/Si Li/Si CONTENT IN RATIO RATIOELECTROLYTE IN POTENTIAL IN POTENTIAL CAPACITY METHOD OF SOLUTION ANODEOF ANODE ANODE OF ANODE RETENTION FORMING (wt. %) (MOLAR VS. Li (MOLARVS. Li RATIO ANODE VC VEC RATIO) (V) RATIO (V) (%) EXAMPLE 1-5 VAPOR — —3.5 0.1 0.46 1.1 95.8 DEPOSITION EXAMPLE 2-1 VAPOR 2 — 3.5 0.1 0.46 1.198.7 DEPOSITION

TABLE 3 AT THE END OF AT THE END OF CHARGE DISCHARGE Li/Si Li/Si CONTENTIN RATIO RATIO ELECTROLYTE IN POTENTIAL IN POTENTIAL CAPACITY METHOD OFSOLUTION ANODE OF ANODE ANODE OF ANODE RETENTION FORMING (wt. %) (MOLARVS. Li (MOLAR VS. Li RATIO ANODE VC VEC RATIO) (V) RATIO) (V) (%)EXAMPLE 1-6 VAPOR — — 3.7 0.08 0.46 1.1 90.4 DEPOSITION EXAMPLE 2-2VAPOR 15 — 3.7 0.08 0.46 1.1 94.2 DEPOSITION EXAMPLE 2-3 VAPOR — 15 3.70.08 0.46 1.1 94.0 DEPOSITION

As shown in Tables 2 and 3, in Examples 2-1 through 2-3 in which acyclic carbonate having an unsaturated bond such as 1,3-dioxol-2-one or4-vinyl-1,3-dioxolane-2-one was added, a higher capacity retention ratiowas obtained, compared to Examples 1-5 and 1-6. In other words, it wasfound out that when a cyclic carbonate having an unsaturated bond wasadded to the electrolyte solution, the cycle characteristics could befurther improved.

Examples 3-1 through 3-10

Secondary batteries were formed as in the case of Example 1-1, exceptthat the composition of the electrolyte solution was changed. As theelectrolyte solution, an electrolyte solution formed through mixingethylene carbonate (EC), 4-fluoro-1,3-dioxolane-2-one (FEC), dimethylcarbonate (DMC), diethyl carbonate (DEC) or 1,3-dioxol-2-one (VC) at amass ratio shown in Table 4 to form a solvent, and then dissolving LiPF₆in the solvent at a concentration of 1 mol/l was used.

A charge-discharge test was carried out on the secondary batteries ofExamples 3-1 through 3-10 as in the case of Example 1-1 to determinetheir capacity retention ratios in the 100th cycle and measure the Li/Siratio in the anode 14 and the potential of the anode 14 vs. Li aftercharge under the above conditions and after discharge under the aboveconditions. The obtained results are shown in Table 4 together with theresults of Example 1-1. The Li/Si ratio in the anode 14 and thepotential of the anode 14 vs. Li at the end of charge and at the end ofdischarge were the same as those in Example 1-1, although they are notshown in Table 4. TABLE 4 COMPOSITION CAPACITY METHOD OF OF SOLVENTRETENTION FORMING (MASS RATIO) RATIO ANODE EC FEC DMC DEC VC (%) EXAMPLE1-1 VAPOR 1.0 0 1.0 0 0 70.1 DEPOSITION EXAMPLE 3-1 VAPOR 0.95 0.05 1.00 0 97.2 DEPOSITION EXAMPLE 3-2 VAPOR 0.9 0.1 1.0 0 0 97.6 DEPOSITIONEXAMPLE 3-3 VAPOR 0.7 0.3 1.0 0 0 97.8 DEPOSITION EXAMPLE 3-4 VAPOR 0.50.5 1.0 0 0 99.2 DEPOSITION EXAMPLE 3-5 VAPOR 0.2 0.8 1.0 0 0 99.2DEPOSITION EXAMPLE 3-6 VAPOR 0 1.0 1.0 0 0 99.2 DEPOSITION EXAMPLE 3-7VAPOR 0 1.0 0 1.0 0 99.1 DEPOSITION EXAMPLE 3-8 VAPOR 0.6 0.6 0.4 0.4 097.8 DEPOSITION EXAMPLE 3-9 VAPOR 0 1.0 0 0 0 97.4 DEPOSITION EXAMPLE3-10 VAPOR 0.45 0.5 1.0 0 0.05 99.2 DEPOSITION

As shown in Table 4, it was found out that in Examples 3-1 through 3-10in which 4-fluoro-1,3-dioxolane-2-one was used, a higher capacityretention ratio was obtained, compared to Example 1-1. In other words,it was found out that when a carbonate derivative containing a halogenatom was used in the electrolyte solution, the cycle characteristicscould be further improved.

Examples 4-1 through 4-8

Secondary batteries were formed as in the case of Example 1-1, exceptthat the composition of the electrolyte solution was changed. In theelectrolyte solution, the same solvent as that in Examples 4-2 through4-6 was used, and the kind of the lithium salt was changed as shown inTable 5. A charge-discharge test was carried out on the secondarybatteries of Examples 4-1 through 4-8 as in the case of Example 1-1 todetermine their capacity retention ratios in the 100th cycle and measurethe Li/Si ratio in the anode 14 and the potential of the anode 14 vs. Liafter charge under the above conditions and after discharge under theabove conditions. The obtained results are shown in Table 5 togetherwith the results of Examples 4-2 through 4-6. The Li/Si ratio in theanode 14 and the potential of the anode 14 vs. Li at the end of chargeand at the end of discharge were the same as those in Example 1-1,although they are not shown in Table 5. TABLE 5 COMPOSITION CAPACITYMETHOD OF OF SOLVENT RETENTION FORMING (MASS RATIO) LITHIUM SALT RATIOANODE EC FEC DMC DEC VC (mol/l) (%) EXAMPLE 3-2 VAPOR 0.9 0.1 1.0 0 0LiPF₆: 1.0 97.6 DEPOSITION EXAMPLE 4-1 VAPOR 0.9 0.1 1.0 0 0 LiPF₉: 0.997.8 DEPOSITION Li(CF₃SO₂)₂N: 0.1 EXAMPLE 3-3 VAPOR 0.7 0.3 1.0 0 0LiPF₆: 1.0 97.8 DEPOSITION EXAMPLE 4-2 VAPOR 0.7 0.3 1.0 0 0 LiPF₆: 0.998.0 DEPOSITION Li(CF₃SO₂)₂N: 0.1 EXAMPLE 3-4 VAPOR 0.5 0.5 1.0 0 0LiPF₆: 1.0 99.2 DEPOSITION EXAMPLE 4-3 VAPOR 0.5 0.5 1.0 0 0 LiPF₆: 0.999.2 DEPOSITION Li(CF₃SO₂)₂N: 0.1 EXAMPLE 4-4 VAPOR 0.5 0.5 1.0 0 0LiPF₆: 0.9 99.2 DEPOSITION CHEMICAL FORMULA 2: 0.1 EXAMPLE 4-5 VAPOR 0.50.5 1.0 0 0 LiPF₆: 0.9 99.0 DEPOSITION CHEMICAL FORMULA 1: 0.1 EXAMPLE3-5 VAPOR 0.2 0.8 1.0 0 0 LiPF₆: 1.0 99.2 DEPOSITION EXAMPLE 4-6 VAPOR0.2 0.8 1.0 0 0 LiPF₆: 0.8 99.2 DEPOSITION Li(CF₃SO₂)₂N: 0.1 CHEMICALFORMULA 2: 0.1 EXAMPLE 4-7 VAPOR 0.2 0.8 1.0 0 0 LiPF₆: 0.9 99.2DEPOSITION Li(C₂F₅SO₂)₂N: 0.05 CHEMICAL FORMULA 1: 0.05 EXAMPLE 3-6VAPOR 0 1.0 1.0 0 0 LiPF₆: 1.0 99.2 DEPOSITION EXAMPLE 4-8 VAPOR 0 1.01.0 0 0 LiPF₆: 0.9 99.2 DEPOSITION Li(CF₃SO₂)₂N: 0.1Chemical Formula 1: lithium bis(oxalato) borateChemical Formula 2: lithium difluoro[oxalato-O,O′] borate

As shown in Table 5, it was found out that even if other lithium saltswere used, the same results could be obtained.

Examples 5-1 through 5-8

Secondary batteries of Examples 5-1 and 5-2 were formed as in the caseof Examples 1-1 through 1-6, except that the anode 14 was formed by asintering method. The anode 14 was formed as follows. At first, 90 wt %of silicon powder with an average particle diameter of 1 μm as an anodeactive material and 10 wt % of polyvinylidene fluoride as a binder weremixed to prepare a mixture, and the mixture was dispersed inN-methyl-2-pyrrolidone as a dispersion medium to form mixture slurry.Next, after the mixture slurry was applied to the anode currentcollector 14A made of electrolytic copper foil with a thickness of 18μm, dried and pressurized, the mixture slurry was heated for 12 hours at400° C. under a vacuum atmosphere to form the anode active materiallayer 14B.

A secondary battery of Example 5-3 was formed as in the case of Example5-2, except that the same electrolyte solution as that in Example 2-1was used. More specifically, an electrolyte solution including 2 wt % of1,3-dioxol-2-one (VC) was used.

Secondary batteries of Examples 5-4 through 5-8 were formed as in thecase of Examples 5-2, except that the same electrolyte solution as thatin Examples 3-1 through 3-5 was used. More specifically, as the solvent,a mixture including ethylene carbonate (EC),4-fluoro-1,3-dioxolane-2-one (FEC) and dimethyl carbonate (DMC) wasused, and the content of 4-fluoro-1,3-dioxolane-2-one was changed.

Moreover, as Comparative Example 5-1 relative to Examples 5-1 and 5-2, asecondary battery was formed as in the case of Examples 5-1 and 5-2,except that the molar ratio of the cathode active material to the anodeactive material was changed.

A charge-discharge test was carried out on the secondary batteries ofExamples 5-1 through 5-8 and Comparative Example 5-1 to determine theircapacity retention ratios in the 100th cycle and measure the Li/Si ratioin the anode 14 and the potential of the anode 14 vs. Li after chargeunder the above conditions and after discharge under the aboveconditions. The obtained results are shown in Tables 6 through 8. InTable 8, the Li/Si ratio in the anode 14 and the potential of the anode14 vs. Li at the end of charge and at the end of discharge are notshown; however, they were the same in each example as those in Example5-2. TABLE 6 AT THE END AT THE END OF OF CHARGE DISCHARGE Li/Si Li/SiRATIO IN POTENTIAL RATIO IN POTENTIAL CAPACITY METHOD OF ANODE OF ANODEANODE OF ANODE RETENTION FORMING (MOLAR VS. Li (MOLAR VS. Li RATIO ANODERATIO (V) RATIO (V) (%) EXAMPLE 5-1 SINTERING 3.95 0.05 0.41 1.3 71.4EXAMPLE 5-2 SINTERING 3.5 0.1 0.42 1.25 76.7 COMPARATIVE SINTERING 4.30.01 0.42 1.25 33.9 EXAMPLE 5-1Electrolyte solution: EC + DMC + LiPF₆

TABLE 7 AT THE END OF AT THE END OF CHARGE DISCHARGE Li/Si Li/Si RATIORATIO METHOD OF IN POTENTIAL IN POTENTIAL CAPACITY OF CONTENT ANODE OFANODE ANODE OF ANODE RETENTION FORMING OF VC (MOLAR VS. Li (MOLAR VS. LiRATIO ANODE (wt%) RATIO) (V) RATIO) (V) (%) EXAMPLE 5-2 SINTERING — 3.50.1 0.42 1.25 76.7 EXAMPLE 5-3 SINTERING 2 3.5 0.1 0.42 1.25 87.3

TABLE 8 COMPOSITION OF CAPACITY METHOD OF SOLVENT RETENTION FORMING(MASS RATIO) RATIO ANODE EC FEC DMC (%) EXAMPLE 5-2 SINTERING 1.0 0 1.076.7 EXAMPLE 5-4 SINTERING 0.95 0.05 1.0 85.0 EXAMPLE 5-5 SINTERING 0.90.1 1.0 91.0 EXAMPLE 5-6 SINTERING 0.7 0.3 1.0 93.0 EXAMPLE 5-7SINTERING 0.5 0.5 1.0 96.0 EXAMPLE 5-8 SINTERING 0.2 0.8 1.0 98.0

As shown in Tables 6 through 8, in Examples 5-1 through 5-8, the sameresults as those in Examples 1-1 through 1-6, 2-1 and 3-1 through 3-5 inwhich the anode 14 was formed by vapor deposition were obtained. Inother words, it was found out that even in the case where the anode 14was formed by a sintering method, when the Li/Si ratio in the anode 14at the end of charge was 4.0 or less or the potential of the anode 14vs. Li at the end of charge was 0.04 V or more, and the Li/Si ratio inthe anode 14 at the end of discharge was 0.4 or more or the potential ofthe anode 14 vs. Li at the end of discharge was 1.4 V or less, the cyclecharacteristics could be improved. Moreover, it was found out that whena cyclic carbonate having an unsaturated bond or a carbonate derivativecontaining a halogen atom was used in the electrolyte solution, thecycle characteristics could be further improved.

Example 6-1

A secondary battery was formed as in the case of Examples 1-1 through1-6, except that the anode 14 was formed by a coating method. The anode14 was formed as follows. At first, 80 wt % of silicon power with anaverage particle diameter of 1 μm as an anode active material, 10 wt %of polyvinylidene fluoride as a binder and 10 wt % of flake naturalgraphite as an electrical conductor were mixed to prepare a mixture, andthe mixture was dispersed in N-methyl-2-pyrrolidone as a dispersionmedium to form mixture slurry. Next, after the mixture slurry wasapplied to the anode current collector 14A made of electrolytic copperfoil with a thickness of 18 μm, dried and pressurized, the mixtureslurry was dried for 5 hours at 100° C. under a vacuum atmosphere toform the anode active material layer 14B. Moreover, as ComparativeExample 6-1 relative to Example 6-1, a secondary battery was formed asin the case of Example 6-1, except that the molar ratio of the cathodeactive material to the anode active material was changed.

A charge-discharge test was carried out on the secondary batteries ofExample 6-1 and Comparative Example 6-1 as in the case of Examples 1-1through 1-6 to determine their capacity retention ratios in the 100thcycle and measure the Li/Si ratio in the anode 14 and the potential ofthe anode 14 vs. Li after charge under the above conditions and afterdischarge under the above conditions. The obtained results are shown inTable 9. TABLE 9 AT THE END OF AT THE END OF CHARGE DISCHARGE Li/SiLi/Si RATIO IN POTENTIAL RATIO IN POTENTIAL CAPACITY METHOD OF ANODE OFANODE ANODE OF ANODE RETENTION FORMING (MOLAR VS. Li (MOLAR VS. Li RATIOANODE RATIO) (V) RATIO) (V) (%) EXAMPLE 6-1 COATING 3.5 0.1 0.46 1.156.8 COMPARATIVE COATING 4.05 0.01 0.41 1.3 12.5 EXAMPLE 6-1Electrolyte solution: EC + DMC + LiPF₆

It was obvious from Table 9 that in Example 6-1, a higher capacityretention ratio was obtained, compared to Comparative Example 6-1. Inother words, it was found out that even in the case where the anode 14was formed by a coating method, when the Li/Si ratio in the anode 14 atthe end of charge was 4.0 or less or the potential of the anode 14 vs.Li at the end of charge was 0.04 V or more, and the Li/Si ratio in theanode 14 at the end of discharge was 0.4 or more or the potential of theanode 14 vs. Li at the end of discharge was 1.4 V or less, the cyclecharacteristics could be improved.

Examples 7-1 through 7-3

Secondary batteries were formed as in the case of Examples 1-1 through1-6, except that the composition of the anode active material layer 14Bwas changed as shown in Table 10. More specifically, the anode activematerial layer 14B was formed of SiW in Example 7-1, Si₄Cu in Example7-2 and Si_(0.99)B_(0.01) in Example 7-3 by a vapor deposition method.They are indicated by a molar ratio.

A charge-discharge test was carried out on the secondary batteries ofExamples 7-1 through 7-3 as in the case of Examples 1-1 through 1-6 todetermine their initial discharge capacities and their capacityretention ratios in the 100th cycle and measure the Li/Si ratio in theanode 14 and the potential of the anode 14 vs. Li after charge under theabove conditions and after discharge under the above conditions. Theobtained results are shown in Table 10 together with the results ofExample 1-2. TABLE 10 AT THE END OF AT THE END OF CHARGE DISCHARGE Li/SiLi/Si ANODE RATIO IN POTENTIAL RATIO IN POTENTIAL CAPACITY INITIALACTIVE ANODE OF ANODE ANODE OF ANODE RETENTION DISCHARGE MATERIAL (MOLARVS. Li (MOLAR VS. Li RATIO CAPACITY LAYER RATIO) (V) RATIO) (V) (%)(mAh/G) EXAMPLE 7-1 SiW 3.92 0.08 0.41 1.3 73.5 1805 EXAMPLE 7-2 Si₄Cu3.92 0.08 0.41 1.3 72.1 2654 EXAMPLE 7-3 Si_(0.99)B_(0.01) 3.95 0.050.41 1.3 71.0 3527 EXAMPLE 1-2 Si 3.95 0.05 0.41 1.3 71.4 3570

As shown in Table 10, in Examples 7-1 through 7-3, superior results wereobtained as in the case of Example 1-2. In other words, it was found outthat in the case where the anode active material layer 14B includedanother element in addition to silicon, when the Li/Si ratio in theanode 14 or the potential of the anode 14 vs. Li were as describedabove, the cycle characteristics could be improved.

Moreover, when the content of silicon in the anode active material layer14B was reduced, there was a tendency of the capacity retention ratio tobe improved; however the capacity declined. In other words, it was foundout that the content of silicon in the anode active material layer 14Bwas preferably 50 mol % or more, more preferably 75 mol % or more andmore preferably 90 mol %.

Example 8-1

A winding type secondary battery shown in FIGS. 2 and 3 was formed. Atfirst, the cathode 31 was formed as in the case of Examples 1-1 through1-5, and the anode 32 was formed through forming the anode activematerial layer 32B made of silicon with a thickness of 3 μm on the anodecurrent collector 32A made of electrolytic copper foil by electron beamevaporation. Next, 10 wt % of polyvinylidene fluoride as a blockcopolymer with a weight-average molecular weight of 600,000 and 60 wt %of dimethyl carbonate as a solvent of a polymeric material were mixed toand dissolved in 30 wt % of an electrolyte solution including 40 wt % ofγ-butyrolactone (γ-BL), 40 wt % of ethylene carbonate (EC), 5 wt % of1,3-dioxol-2-one (VC) and 15 wt % of LiPF₆ to form a precursor solution.Then, the precursor solution was applied to each of the cathode 31 andthe anode 32, the cathode 31 and the anode 32 were left for 8 hours atroom temperature to volatilize dimethyl carbonate, thereby theelectrolyte layer 34 was formed on the cathode 31 and the anode 32.

Next, the cathode 31 on which the electrolyte layer 34 was formed andthe anode 32 on which the electrolyte layer 34 was formed were cut intoa strip shape, and the lead 21 was attached to the cathode 31, and thelead 22 was attached to the anode 32. After that, the cathode 31 onwhich the electrolyte layer 34 was formed and the anode 32 on which theelectrolyte layer 34 was formed were laminated with the separator 33 inbetween to form a laminate body, and the laminate body was spirallywound to form the spirally wound electrode body 30. Then, the spirallywound electrode body 30 was covered with the package members 41 and 42.

As Comparative Example 8-1 relative to Example 8-1, a secondary batterywas formed as in the case of Example 8-1, except that the molar ratio ofthe cathode active material to the anode active material was changed.

A charge-discharge test was carried out on the secondary batteries ofExample 8-1 and Comparative Example 8-1 as in the case of Example 1-1through 1-6 to determine their capacity retention ratios in the 100thcycle and measure the Li/Si ratio in the anode 32 and the potential ofthe anode 32 vs. Li after charge under the above conditions and afterdischarge under the above conditions. At that time, the Li/Si ratio inthe anode 32 and the potential of anode 32 vs. Li were measured by usingthe circular shaped anode 32 which was formed through stamping a centralportion of the anode 32 into a circular shape with a diameter of 15 mm.The results are shown in Table 11. TABLE 11 AT THE END OF AT THE END OFCHARGE DISCHARGE Li/Si Li/Si RATIO IN POTENTIAL RATIO IN POTENTIALCAPACITY METHOD OF ANODE OF ANODE ANODE OF ANODE RETENTION FORMING(MOLAR VS. Li (MOLAR VS. Li RATIO ANODE RATIO) (V) RATIO) (V) (%)EXAMPLE 8-1 VAPOR 3.6 0.12 0.41 1.3 80.3 DEPOSITION COMPARATIVE VAPOR4.05 0.01 0.41 1.3 44.1 EXAMPLE 8-1 DEPOSITIONElectrolyte: γ − BL + EC + VC + LiPF₆ + PVDF

As shown in Table 11, in Example 8-1, a higher capacity retention ratiowas obtained, compared to Comparative Example 8-1. In other words, itwas found out that even in the case where a so-called gel electrolytewas used, or even in the case where the cathode 31 and the anode 32 werespirally wound, when the Li/Si ratio in the anode 32 or the potential ofthe anode 32 vs. Li were as described above, the cycle characteristicscould be improved.

Examples 9-1 through 9-9

Secondary batteries were formed as in the case of Example 8-1, exceptthat the composition of the electrolyte solution was changed. As theelectrolyte solution, an electrolyte solution formed through mixingethylene carbonate (EC), 4-fluoro-1,3-dioxolane-2-one (FEC) or1,3-dioxol-2-one (VC) at a mass ratio shown in Table 12 to form asolvent, and then dissolving the lithium salt in the solvent at aconcentration of 1 mol/l was used. The kind of the lithium salt waschanged as shown in Table 12.

The secondary batteries of Examples 9-1 through 9-9 and Example 8-1 werecharged and discharged under the same conditions as those in Example 1-1to examine the storage characteristics. More specifically, 10charge-discharge cycles were carried out to determine the dischargecapacity in the 10th cycle as a capacity before storage. Then, thesecondary batteries were charged again, and the secondary batteries werestored for 20 days at 70° C., and then the secondary batteries weredischarged. Next, one charge-discharge cycle was carried out again todetermine the discharge capacity as a capacity after storage. As thestorage characteristics, a ratio of the capacity after storage to thecapacity before storage, that is, (the capacity after storage/thecapacity before storage)×100 was determined as a capacity retentionratio after storage. The obtained results are shown in Table 12. TABLE12 CAPACITY RE- TENTION COMPOSITION OF RATIO SOLVENT AFTER (MASS RATIO)LITHIUM SALT STORAGE EC FEC VC (mol/l) (%) EXAMPLE 9-1 0.45 0.5 0.05LiPF₆: 1.0 88 EXAMPLE 9-2 0.9 0.1 0 LiPF₆: 0.9 87 Li(CF₃SO₂)₂N: 0.1EXAMPLE 9-3 0.7 0.3 0 LiPF₆: 0.9 88 Li(CF₃SO₂)₂N: 0.1 EXAMPLE 9-4 0.50.5 0 LiPF₆: 0.9 89 Li(CF₃SO₂)₂N: 0.1 EXAMPLE 9-5 0.5 0.5 0 LiPF₆: 0.987 CHEMICAL FORMULA 2: 0.1 EXAMPLE 9-6 0.5 0.5 0 LiPF₆: 0.9 88 CHEMICALFORMULA 1: 0.1 EXAMPLE 9-7 0.2 0.8 0 LiPF₆: 0.8 91 Li(CF₃SO₂)₂N: 0.1CHEMICAL FORMULA 2: 0.1 EXAMPLE 9-8 0.2 0.8 0 LiPF₆: 0.9 88Li(C₂F₅SO₂)₂N: 0.05 CHEMICAL FORMULA 1: 0.05 EXAMPLE 9-9 0 1.0 0 LiPF₆:0.9 86 Li(CF₃SO₂)₂N: 0.1 EXAMPLE 8-1 Electrolyte: γ-BL + EC + VC + LiPF₆67Chemical Formula 1: lithium bis(oxalato) borateChemical Formula 2: lithium difluoro[oxalato-O,O′] borate

As shown in Table 12, in Examples 9-1 through 9-9 in which4-fluoro-1,3-dioxolane-2-one was used, a higher capacity retention ratiowas obtained, compared to Example 8-1. In other words, it was found outthat when a carbonate derivative containing a halogen atom was used inthe electrolyte solution, the storage characteristics could be improved.

Although the invention is described referring to the embodiment and theexamples, the invention is not limited to them, and is variouslymodified. For example, in the embodiment and the examples, the casewhere a polymeric material is used as a holding body is described;however, an inorganic conductor including lithium nitride or lithiumphosphate may be used as a holding body, or a mixture including apolymeric material and an inorganic conductor may be used.

Moreover, in the embodiment and the examples, the coin-type secondarybattery and the winding laminate type secondary battery is described;however, the invention is also applicable to secondary batteries with acylindrical shape, a prismatic shape, a button shape, a thin shape, alarge shape and a laminate shape in a like manner. Further, theinvention is applicable to not only the secondary batteries but alsoother batteries such as primary batteries.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

1. A battery, comprising: an anode including silicon (Si) as an elementand being capable of inserting and extracting lithium (Li); a cathodebeing capable of inserting and extracting lithium; and an electrolyte,wherein a molar ratio of lithium atoms to silicon atoms (Li/Si) in theanode is 4.0 or less.
 2. A battery according to claim 1, wherein a molarratio of lithium atoms to silicon atoms (Li/Si) in the anode is 0.4 ormore.
 3. A battery according to claim 1, wherein the anode includes ananode current collector and an anode active material layer beingdisposed on the anode current collector, including silicon as anelement, and being alloyed with the anode current collector at at leasta part of an interface with the anode current collector.
 4. A batteryaccording to claim 1, wherein the anode includes an anode currentcollector and an anode active material layer being formed on the anodecurrent collector by at least one method selected from the groupconsisting of a vapor-phase deposition method, a liquid-phase depositionmethod and a sintering method, and including silicon as an element.
 5. Abattery according to claim 1, wherein the electrolyte includes at leastone kind selected from the group consisting of a cyclic carbonate havingan unsaturated bond and a carbonate derivative containing a halogenatom.
 6. A battery, comprising: an anode including silicon (Si) as anelement and being capable of inserting and extracting lithium (Li); acathode being capable of inserting and extracting lithium; and anelectrolyte, wherein a potential of the anode vs. lithium metal as areference po tential is 0.04 V or more.
 7. A battery according to claim6, wherein a potential of the anode vs. lithium metal as a referencepotential is 1.4 V or less.
 8. A battery according to claim 6, whereinthe anode includes an anode current collector and an anode activematerial layer being disposed on the anode current collector, includingsilicon as an element, and being alloyed with the anode currentcollector at at least a part of an interface with the anode currentcollector.
 9. A battery according to claim 6, wherein the anode includesan anode current collector and an anode active material layer beingformed on the anode current collector by at least one method selectedfrom the group consisting of a vapor-phase deposition method, aliquid-phase deposition method and a sintering method, and includingsilicon as an element.
 10. A battery according to claim 6, wherein theelectrolyte includes at least one kind selected from the groupconsisting of a cyclic carbonate having an unsaturated bond and acarbonate derivative containing a halogen atom.
 11. A method of chargingand discharging a battery, the battery comprising an anode whichincludes silicon (Si) as an element and is capable of inserting andextracting lithium (Li), wherein at the time of charge, a molar ratio oflithium atoms to silicon atoms (Li/Si) in the anode is 4.0 or less. 12.A method of charging and discharging a battery according to claim 11,wherein at the time of discharge, a molar ratio of lithium atoms tosilicon atoms (Li/Si) in the anode is 0.4 or more.
 13. A method ofcharging and discharging a battery, the battery comprising an anodewhich includes silicon (Si) as an element and is capable of insertingand extracting lithium (Li), wherein a potential of the anode vs.lithium metal as a reference potential at the time of charge is 0.04 Vor more.
 14. A method of charging and discharging a battery according toclaim 13, wherein a potential of the anode vs. lithium metal as areference potential at the time of discharge is 1.4 V or less.
 15. Acharge-discharge control device for a battery, the battery comprising ananode which includes silicon (Si) as an element and is capable ofinserting and extracting lithium (Li), the charge-discharge controldevice comprising. a charge control portion for controlling a molarratio of lithium atoms to silicon atoms (Li/Si) in the anode at the timeof charge to 4.0 or less.
 16. A charge-discharge control device for abattery according to claim 15, further comprising: a discharge controlportion for controlling a molar ratio of lithium atoms to silicon atoms(Li/Si) in the anode at the time of discharge to 0.4 or more.
 17. Acharge-discharge control device for a battery, the battery comprising ananode which includes silicon as an element and is capable of insertingand extracting lithium (Li), the charge-discharge control devicecomprising: a charge control portion for controlling a potential of theanode vs. lithium metal as a reference potential at the time of chargeto 0.04 V or more.
 18. A charge-discharge control device for a batteryaccording to claim 17, further comprising: a discharge control portionfor controlling a potential of the anode vs. lithium metal as areference potential at the time of discharge to 1.4 V or less.